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Is it possible to build a device in which the forward motion turns a wheel that turns a propeller which provides enough wind propulsion to accelerate the device forward faster than the air around it? You would think not, but some investigators appear to have accomplished just that.

I talked with Spork33 today, after posting the above. He's the person featured in several of the DDFTTW videos.

He is convinced that existing laws of aerodynamics can explain this phenomena, and he is in process of composing a scientific paper for publication in a refereed journal that will detail the mechanics involved.

Bear in mind that you will not be able to just plop this on a flat surface such as a gym floor, give it a good push, and it take off accelerating. The device on the treadmill is analogous to a cart going along with a tail wind of the same speed, and the mechanism makes it go faster than the tail wind. He said he has been assembling about 20 of these to ship out to a few people (primarily skeptics) from various forums who have asked to replicate the effect. He said that in doing several at once, the parts run around $40.00 USD. He asks another $5.00 for shipping. So at this juncture he's only doing it on a limited basis for scientific advancement. At that price, he's not willing to make very many.

Until the thing is mass produced, it will be fairly expensive. We (PES Network, Inc.) are in discussion with him about entering into an agreement to build and ship kits with adequate mark-up to make it worth our while, e.g. $80 retail. If you are interested (customer side or business side), please send an email to DDWFTTW.kit@pureenergysystems.com .

Because the gadget won't accelerate across a flat surface but will only move forward on a treadmill, the number of people wanting one will probably be fairly low, and the practical aspects perhaps lower yet.

It certainly is a scientific curiosity. Perhaps the principles underlying it may eventually spur some significant aerodynamic advancements in efficiency.

Given access to two streams with parallel velocities (relative to you)

What 2 streams do you exactly mean ?Can you explain it some more ?

It seems from the videos, that it only depends how fast the wheelsare rotating and this is geared up to the propeller.

So from the test videos on the threadmillit seems, that this device only needs to be pushed up to 10 miles/hour speedand then it will accelerate itsself without needing any blowing wind itsself to speed up.All is probably done via the right combination of the right wheel to propeller gear ratio.

Then it seems to overcome friction and seems to selfaccelerate.

So it seems one could build cars like this, that just onlyneed a motor to push them over the 10 miles/hour thresholdand then you could switch off the motor and the car wouldselfaccelerate. Amazing !

Even a propellor with zero pitch, once started, should continue turning, as the 'virtual surface area' is increased with velocity. The fact that the prop still works when pitched to provide a modicum of thrust against the tail wind, demonstrates how effective a small surface area can be at creating said increase in 'virtual surface area' when moving perpendicular to the flow of wind.

This still does not fully account for the slight force asymmetry expressed in the higher vehicle velocity, which is why I propose duplicating the experiment with winglets on the prop tips.

It seems plausible that VRS (vortex ring state) may be involved....producing a small area of low pressure ahead of the craft. If such is the case, winglets of sufficient size at the prop tips will serve to modify velocity differentials.

My main concern is that the fellow said you can't just put this on a flat surface like a gym floor and have it work..it works on the treadmill. This I do not understand. When learning to fly and also building my own small airboat, I had a chance to learn a little about propellers. The main principle I see here is that when a propeller is turning, the relative wind sees it as a solid disk. Now, this only applies when the prop, depending on the pitch and airfoil design, is turning faster than the relative wind, or slower. There is an equilibrium point for all propellers at a certain rpm in a certain relative wind that adds 0 drag and 0 thrust, but this is a small window. They use this when they teach you to land simulating an "engine out" experience. If you just set the engine to idle, the drag produced by the prop would be way higher than in a real engine out scenario, and therefore would be of little use for learning to deal with a real one.

So, I can see where you have a 10 mph tailwind, and the prop is turning via the wheels after an initial push, so the prop then acts as a parachute or sail to catch the tailwind and push the craft faster. Once it reaches the speed of the tailwind, as Stefan said, through proper gear ratios, the propeller turns at its designed rpm and therefore produces thrust which makes it go faster than the wind. All of this works for me with what I know except it not running on a flat surface like a gym floor. This part, I can not explain at all.

My main concern is that the fellow said you can't just put this on a flat surface like a gym floor and have it work..it works on the treadmill. This I do not understand. When learning to fly and also building my own small airboat, I had a chance to learn a little about propellers. The main principle I see here is that when a propeller is turning, the relative wind sees it as a solid disk. Now, this only applies when the prop, depending on the pitch and airfoil design, is turning faster than the relative wind, or slower. There is an equilibrium point for all propellers at a certain rpm in a certain relative wind that adds 0 drag and 0 thrust, but this is a small window. They use this when they teach you to land simulating an "engine out" experience. If you just set the engine to idle, the drag produced by the prop would be way higher than in a real engine out scenario, and therefore would be of little use for learning to deal with a real one.

So, I can see where you have a 10 mph tailwind, and the prop is turning via the wheels after an initial push, so the prop then acts as a parachute or sail to catch the tailwind and push the craft faster. Once it reaches the speed of the tailwind, as Stefan said, through proper gear ratios, the propeller turns at its designed rpm and therefore produces thrust which makes it go faster than the wind. All of this works for me with what I know except it not running on a flat surface like a gym floor. This part, I can not explain at all.

Bill

Hi Bill,

The whole things a bit of a mind bender. ItÂ´s an impressive device and appears to do something that many people say is impossible which is always a good thing to do!

The only thing I can think of is that on the treadmill, the craft does not see an oncoming airstream and thus sees no air friction. Wheras if you push it along a gym floor it would have to overcome the oncoming air resistance.

Also, I think this craft enables one to move a certain percentage faster than the driving wind, that percentage might vary and have a sweet spot of wind speed where you get the best gain, but in the case of 0mph wind as in a gym then that percentage will be zero so it wont sustain motion. To simulate the gym floor using the treadmill one would have to face the treadmill into a wind that matched the treadmill speed.

P.S.impressed that you built an airboat! model planes and helis are as far as IÂ´ve gone.

I thought this was pretty easy to figure out, on the treadmill the device produces near balanced forces, that is thrust nearly equals drag from the driving components or ground speed nearly equals generated air speed. But if this device is travelling with the wind behind it something really neat happens. To understand this I think you have to concentrate on relative motion and the neutral point of force. If the tail wind speed is 5mph pushing the craft forward then when the craft reaches 5mph ground speed the apparent wind you would "feel" is now zero mph so there is very little air resistance. Also if the ground speed is 5mph or equal to the tail wind speed then directly behind the prop there is a point of zero windspeed which constitutes a pressure boundary.(Wind) 5mph----->zero<-----5mph(propeller)One analogy could be standing in an elevator moving upwards at 5mph and jumping upwards at 2mph, you "feel" a 2mph velocity(apparent) but you are moving upwards at 7mph(reality). The reason this can happen is because you are "in an elevator", if you were not in an elevator you would have nothing to push against to jump. We can say that the only reason this craft can exceed the wind speed is because the prop generated wind has something to push against and this something is a wall of "pressure" having an apparent velocity of zero mph but having a real ground speed equal to the craft. A good analogy is having the launch pad of a rocket accelerating behind the rocket but not being attached to it, in this case we are not dealing strictly with reactive mass, we are dealing with a wall of pressure acting in the same direction of acceleration because the gasses ejected from the rocket are pushing against a boundary or obstruction. In this device the forces would look something like this--(wind) 5mph----->Zero<----------- 7mph(propeller)----->2mph Total = (wind) 5mph---> + 2mph----> = 7mph ground speed = 7 mph thrustAs the ground speed increases so does the thrust generated by the propeller but the propeller does not "push" the craft----the pressure generated behind the craft does and the wind has provided half of the velocity to maintain this pressure wall behind the craft and all of the energy to maintain the velocity of the craft. Regards AC

The principle of this device is very simple and straightforward, the â€œair carâ€ is getting its energy from the treadmill motor. Friction between the wheels and belt turn a shaft that is attached to an angle miter gear that is attached to a second shaft that drives a propeller, thus producing thrust.At the proper rpm the propeller will produce enough thrust to overcome the friction gravity, and drag to move the vehicle forward. But it is not producing its own energy it is getting it from the treadmill.